One typical configuration of proposed power output apparatus mounted on a vehicle has an engine, a planetary gear unit including a carrier linked to an output shaft of the engine and a ring gear linked to an axle of the vehicle, a motor MG1 inputting and outputting power from and to a sun gear of the planetary gear unit, a motor MG2 inputting and outputting power from and to the axle, and a battery being capable of transmitting electric power from and to the motors MG1 and MG2 (see, for example, Japanese Patent Laid-Open Gazette No. H09-308012). This prior art power output apparatus specifies a torque command to be output to the ring gear based on the driver's depression amount of an accelerator pedal and the rotation speed of the ring gear, and calculates the output energy to be output from the engine by summing up the product of the specified torque command and the rotation speed of the ring gear and a charge-discharge electric power that is actually charged into or discharged from the battery. A target rotation speed and a target torque of the engine are set as an optimum drive point to ensure efficient output of the calculated output energy from the engine. A torque command of the motor MG1 is specified to ensure the operation of the engine at the set target rotation speed. A torque command of the motor MG2 is specified by subtracting an amount of torque output from the engine to the ring gear via the planetary gear unit from the specified torque command to be output to the ring gear. The prior art power output apparatus then controls the engine to be driven at a target drive point defined by the combination of the target rotation speed and the target torque, while controlling the motors MG1 and MG2 to be driven with the respectively set torque commands.